CFVCCM9 Compact 9 Line master Exchange UnitCFVCCM9 Compact 9 Line master Exchange Unit An EVCS is a fixed, secure, bi directional, full duplex voice communication system to assist fire fighters in an emergency in high rise buildings or large sites where radio communication may not work, and covers the operation of fire telephones, disabled refuge systems and the Disabled Toilet Alarm. The VoCALL Compact Emergency Voice Communications System (EVCS) is designed to fully comply with BS5839 Part